Generally, the waveform measurement of a light wave having a pulse shape is an essential element in various applications. In order to measure the waveform of a light wave whose electric field changes over time, the amplitude and phase of the light wave should be measured in time domain or frequency domain.
According to the prior art, various methods are used to measure the light wave. One of the most widely used methods for measuring the light wave is using a harmonic radiation generated from a nonlinear material. Among them, autocorrelation is widely used.
In the autocorrelation method, an input light wave is split into two pulses using an optical interferometer, and the two pulses are recombined in a nonlinear material to generate a harmonic radiation. Since the intensity of the harmonic wave increases when two pulses overlap in time domain, the approximate pulse duration of the input light wave may be determined by measuring the intensity of the harmonic wave as a function of time delay between the two pulses.
However, according to the method using the autocorrelation, only information on the pulse duration of the light wave can be obtained. There is no information on the phase of the light wave. Therefore, the waveform of the light wave cannot be measured.
Examples of a method of measuring the amplitude and phase of a spectrum in the frequency domain include a frequency-resolved optical gating (FROG) method and a spectral phase interferometry for direct electric-field reconstruction (SPIDER) method.
In the FROG method and the SPIDER method, similar to the autocorrelation method, the input light wave is divided into two pulses using an optical interferometer, and the spectrum of the harmonic wave generated by recombining the two pulses in the nonlinear material is measured as a function of the time delay between two pulses. When using these methods, it is possible to measure the waveform of the input light wave using the pulse reconstruction algorithm.
However, since the above-described methods measure a light wave based on a harmonic wave generation in a nonlinear material, the above-described methods may be applied only to a specific wavelength that satisfies the phase matching condition of the nonlinear material.
A method for measuring the pulse duration of a light wave using ionization of a material without a wavelength limitation problem of a nonlinear material has been proposed. The conventional light wave measurement methods using multiphoton ionization are performed by dividing a light wave into two pulses and then focusing them on the ionized material and measuring the ionization yield that changes with the time delay between the two pulses. Since these methods correspond to the autocorrelation method in which the ionization yield produced by the light wave is described by multiphoton ionization, there is no information on the phase of the light wave. Therefore, the approximate pulse duration of the light wave can be measured, but the waveform of the light wave cannot be measured.
In the Attosecond streak camera method or the Petahertz optical oscilloscope method, the waveform of a light wave is measured using a high harmonic radiation. However, these methods have a disadvantage in that a complicated high harmonic generation and extreme ultraviolet measurement apparatuses are required.
As a result, the prior light wave measurement methods have the following problems.
In the autocorrelation method, the waveform of the light wave cannot be measured because information on the phase of the light wave is not provided.
Light wave measurement methods using nonlinear materials (autocorrelation method, FROG method, SPIDER method, etc.) may be applied only in a limited wavelength range.
The prior method of measuring the light wave using multiphoton ionization of materials corresponds to the autocorrelation method, so the waveform of the light wave cannot be measured.
The method using high harmonic radiation requires complicated high harmonic generation and extreme ultraviolet measurement apparatuses.
Therefore, there is a need for a technique for measuring the waveform of a light wave in time domain by using a apparatus for overcoming the above-described disadvantages with a simple structure.